Wideband EM coupler/applicator design and characterization for the clinical benchmarking tests of microwave stethoscope (MiSt)

The MiSt is a novel non-invasive vital signs sensor that can simultaneously measure and extract multiple vital signs parameters including the heart rate, respiration rate, heart waveform, and changes in lung water content from a single microwave measurement. The microwave applicator used to couple the microwave signal to the patient´s chest and to measure the reflection from various body tissues play an important role in the MiSt operation for detecting multiple vital signs. In this paper, the design and characterization results of four different broadband electromagnetic couplers and their inherent tradeoffs are presented and discussed. It is shown that it is possible to achieve more than 10:1 bandwidth.